1. Field of the Invention
This invention relates to a variable resistor in which a movable member formed with a resistor is attached to a fixed member having a slider element fixed thereto in such a way that the movable member can be reciprocated, and further the slider element and the resister are brought into sliding contact with each other.
2. Description of the Prior Art
Referring now to FIGS. 12 to 14, this type of variable resistor of the prior art will be described. This variable resistor is comprised of a cylindrical-formed insulating housing 51 acting as a fixed member; an insulating rotary shaft 52 rotatably stored in the housing 51 and acting as a movable member having an engaging part 52a in at least one end thereof to be engaged with a screw driver or the like; a flexible insulating sheet 53 wound around the rotary shaft 52 within the housing 51; a resistance circuit 54 formed at this flexible insulating sheet 53; a slider element 55 attached to the housing 51 is in sliding contact with the resistance circuit 54; and a connecting terminal 56 connected to the slider element 55.
FIG. 13 is a development view for showing the flexible insulating sheet 53 and the resistance circuit 54 arranged in the flexible insulating sheet. FIG. 14 is a sectional view taken along line 14--14 of FIG. 13, wherein the resistance circuit 54 is comprised of one resistor 54a and two electrodes 54b, 54c extending in parallel with a circumferential direction of the rotary shaft 52, and they are connected to each other in series with the resistor 54a being an intermediate one of them. The slider element 55 is comprised of three slider elements 55a, 55b, 55c of which extremity ends are in sliding contact with the resistor 54a and the electrodes 54b, 54c, respectively, and the connecting terminal 56 is comprised of three connecting terminals 56a, 56b, 56c each of which is electrically connected to the slider elements 55a, 55b, 55c, respectively.
The variable resistor constructed as described above is constituted such that when the rotary shaft 52 is turned by a screw driver and the like under a state in which a predetermined voltage is applied between the slider elements 55b, 55c through the connector terminals 56b, 56c, the resistance circuit 54 wound around the rotary shaft 52 is rotationally moved in respect to the slider elements 55a, 55b, 55c and then the sliding contact positions of the slider elements 55a, 55b, 55c on the resistor 54a and the electrodes 54b, 54c are changed. With such an arrangement as above, a resistance value (a voltage value) between the slider elements 55a, 55b and a resistance value (a voltage value) between the slider elements 55a, 55c are changed, an electrical signal (a voltage signal) corresponding to a rotation of the rotary shaft 52 is taken out of the connecting terminal 56a through the slider element 55a.
Then, in the case that the resistance circuit 54 is formed on the flexible insulating sheet 53, it is necessary to provide two steps: an electrode forming step and a resistor forming step, wherein at first, at the electrode forming step, the electrodes 54b, 54c such as a silver foil or a copper foil and the like are adhered by vapor deposition or adhered with adhesive agent, then the resistor 54a such as a beryllium foil, nichrome foil and tungsten foil or the like is adhered by vapor deposition or adhered with adhesive agent to form the resistance circuit 54.
However, in the case of the prior art variable resistor described above, the slider elements 55a, 55b, 55c fixed to the housing 51 slide on the resistor 54a and the electrodes 54b, 54c wound around the rotary shaft 52 under a rotation of the rotary shaft 52. Due to this fact, the prior art needs not only a troublesome step for forming the electrodes 54b, 54c, but also requires the electrode forming step and the resistor forming step, resulting in that an entire manufacturing step for the variable resistor is extend in addition due to the fact that there is present only one resistor 54a and its maximum length merely corresponds to a value of one circumference around the rotary shaft 52, it is not possible to set a rated voltage to high value and so if a high voltage is applied between the slider elements 55b, 55c, there occurs a problem that the resistor 54a is burned.